A’-Pyrazoline-5-ones

PyrazoUne-5-ones. Treatment of 2-bromo-l,3-diphenyl-l,3-propanedione (1) with methylhydrazine in ethanol at room temperature gives l-methyl-3,4-diphenyl-A -pyrazoline-5-one (2) in 56% yield. It is probably formed by a halohydrin rearrangement as indicated. 

Pyrazottne-5-ones Treatment of 5-hydroxy-3,5-diphenyl-A2-pyrazoline-4-one (l)withmethanolicpotassiumhydroxidegives4-hydroxy-3,4-diphcnyl-A -pyrazoline-5-one (2) in 76-80% yield. A pinacol rearrangement is probably involved. Compound (2)... 

It is known that 4-benzal-l-phenyl-A -pyrazolin-5-one reacts both like an heterodiene and an alkene in a Diels-Alder reaction towards 2,3-dimethylbutadiene <88T5229>. The 1,3-dipolar cycloaddition of nitrones to the N//-tautomer of l-phenyl-3-methyl-3-pyrazolin-5-one yields a nonisolated cycloadduct which rearranges to a 4-substituted derivative of the starting material (4-substituent = CH(Ar)— N(Ph)—OH) <94JCR(S)154>. 

A second common reaction of sulphonium ylides is Michael addition to ajS-unsaturated carbonyl compounds, giving cyclopropanes. This reaction forms the basis of a cyclopentene synthesis starting from sulphonium allylide (14). Other recent examples include the preparation of spiro[cyclopropane-l,4-A -pyrazolin]-5 -one derivatives (15) and cyclopropyl-ulose (16). Un-... 

Together with pyridones, the tautomerism of pyrazolones has been studied most intensely and serves as a model for other work on tautomerism (76AHC(Sl)l). 1-Substituted pyrazolin-5-ones (78) can exist in three tautomeric forms, classically known as CH (78a), (DH (78b) and NH (78c). In the vapour phase the CH tautomer predominates and in the solid state there is a strongly H-bonded mixture of OH and HN tautomers (Section 4.04.1.3.1). However, most studies of the tautomerism of pyrazolones correspond to the determination of equilibrium constants in solution (see Figure 20). 

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

The reaction is very common in pyrazolone chemistry. Since alkoxypyrazoles and tautomerizable pyrazolones undergo this reaction and 3-pyrazolin-5-ones, like antipyrine, do not, it is assumed that the reaction takes place at C-4 of the OH tautomer. Pyrazolone diazo coupling is an important industrial reaction since the resulting azo derivatives are used as dyestuffs. For instance, tartrazine (Section 4.04.4.1.3) has been prepared this way. 3,5-Pyrazolidinediones react with aryldiazonium salts resulting in the introduction of a 4-arylazo group. As has been described in Section 4.04.2.1.4(v), diazonium salts couple in the 3-position with indazole to give azo compounds. 

Pyrazolones show a great variety of reactions with carbonyl compounds (B-76MI40402). For instance, antipyrine is 4-hydroxymethylated by formaldehyde and it also undergoes the Mannich reaction. Tautomerizable 2-pyrazolin-5-ones react with aldehydes to yield compound (324) and with acetone to form 4-isopropylidene derivatives or dimers (Scheme 8 Section 4.02.1.4.10). 

A-Oxidation with peracids (Section 4.04.2.1.3) and the transformation of pyrazoles into 4,4-dihalogeno-2-pyrazolin-5-ones (Section 4.04.2.1.4(v)) have already been discussed. Transformation of non-aromatic 2-pyrazolin-5-ones into the 4-oxo derivatives will be examined in Section 4.04.2.2.l(ii). 

Muzolimine (710), a 1-substituted 2-pyrazolin-5-one derivative, is a highly active diuretic, differing from the structures of other diuretics since it contains neither a sulfonamide nor a carboxyl group. It has a saluretic effect similar to furosemide and acts in the proximal tubule and in the medullary portion of the ascending limb of the loop of Henle. Pharmacokinetic studies in dogs, healthy volunteers and in patients with renal insufficiency show that the compound is readily absorbed after oral administration (B-80MI40406). 

Methyl-l-phenyl-3-pyrazolin-5-one gives a green-black dye (736) with 4-nitroso- or 4-amino-dimethylaniline and silver chlorides in the presence of light, a process of great importance in colour photography (B-76MI40403). 

Substituted pyrazolin-5-ones have only three and -substituted pyrazolin-3-ones only two tautomers, since now the corresponding 19c and 19d structures are isomers. The calculations involved l-methylpyrazolin-5-one (PM3/6-3H-G, anions and cations), l-phenyl-3-methyl-2-pyrazolin-5-one (DFT, radical reactions) [97JPC(A)3769], and l-(2, 4 -dinitrophenyl)-3-methyl-2-pyrazolin-5-one [B3LYP/6-31G and the crystal structure (Section V,D,2)] (98NJC1421). 

A mixture of 16.3 g of 4-methyl-6-methoxy-2-pyrimidinyl-hydrazine, 13.7 g of ethyl acetoacetate and 16.3 ml of methanol was refluxed 2 hours on a water bath. After a mixture of 4.7 g of sodium hydroxide, 4.7 ml of water and 27 ml of methanol was added dropwise thereto at about 50°C, the reaction mixture was refluxed for 2 hours more, then methanol was distilled off and the residue was dissolved in 130 ml of water. The solution was adjusted to pH 6 with acetic acid. The precipitate was filtered, washed with water and dried to give 24 g (yield 95.3%) of crystals, MP 97° to 98°C. Recrystallization from ligroin gave 1-(4 -methyl-6 -methoxy-2 -pyrimidinyl)-3-methyl-3-pyrazoline-5-one, MP 102° to 103°C. 

To a solution of 4.76 g of 1-(4 -methyl-6 -methoxy-2 -pyrimidinyl)-3-methyl-3-pyrazoline-5-one in 200 ml of ether was added an ether solution containing 6 molar equivalents of diazomethane and the reaction mixture was allowed to stand at room temperature for 20 hours. After distilling off the solvent, the residue was dissolved in 160 ml of water, made alkaline (pH 10) with sodium hydroxide solution and extracted three times with 140 ml of benzene. The extract was washed with a small amount of water, dried over sodium sulfate and evaporated to give a crystalline mass. Recrystallization from isopropylether gave 1-(4 -methyl-6 -methoxy-2 -pyrimidinyl)-3-methyl-5-methoxypyrazole (3.96 g, 84%) as colorless prisms, MP 90° to 92°C. 

A. 3-(l-Propyl)-2-pyrazolin-5-one. A 500-ml., round-bottomed flask equipped with a magnetic stirring bar and a reflux condenser is charged with 23.7 g. (0.15 mole) of ethyl 3-oxohexanoate (Note 2), 250 ml. of... 

The present method9 affords the methyl ester directly in high yields from 2-pyrazolin-5-ones, which are readily prepared in nearly quantitative yields from readily accessible, /3-keto-esters. In addition, the reaction is simple to carry out, conditions are mild, and the product is easily isolated in a high state of purity. A limitation of the reaction is that only the methyl ester can be made, as other alcohols have been found to give poor yields and undesirable mixtures of products. Table I illustrates other examples of the reaction.10... 

The recently reported (757) conversion of 5-pyrazolones directly to a,j8-acetylenic esters by treatment with TTN in methanol appears to be an example of thallation of a heterocyclic enamine the suggested mechanism involves initial electrophilic thallation of the 3-pyrazolin-5-one tautomer of the 5-pyrazolone to give an intermediate organothallium compound which undergoes a subsequent oxidation by a second equivalent of TTN to give a diazacyclopentadienone. Solvolysis by methanol, with concomitant elimination of nitrogen and thallium(I), yields the a,)S-acetylenic ester in excellent (78-95%) yield (Scheme 35). Since 5-pyrazolones may be prepared in quantitative yield by the reaction of /3-keto esters with hydrazine (168), this conversion represents in a formal sense the dehydration of /3-keto esters. In fact, the direct conversion of /3-keto esters to a,jS-acetylenic esters without isolation of the intermediate 5-pyrazolones can be achieved by treatment in methanol solution first with hydrazine and then with TTN. 

Diethyl N-phenylaminothiocarbonylmalonate was reacted with hydrazine hydrate in boiling ethanol for 4 hr to give a mixture of 5-phenylamino-2-pyrazolin-5-one and monoethyl ester, a hydrazide of hydrazino(phe-nylamino)methylenepropanedioic acid (77G555). 

A solution of methylhydrazine in methanol was added dropwise to a solution of dimethyl methoxymethylenemalonate in methanol. The initial reaction was exothermic, and the rate of addition was controlled to achieve reflux. The reaction mixture was kept boiling for an additional 4 hr to give pyrazolecarboxylate (1327) in 81% yield (88JOC810). Arylhydrazono-methylenemalonates gave l-aryl-2-pyrazolin-5-ones in boiling aqueous sodium hydroxide for 12 hr (87GEP3617554). 

Cyclocondensation of 3-amino-2-pyrazolin-5-ones (22) with )S-diketones affords either pyrazolo[3,4-d]pyridines 23 or pyrazolo[l,5-a]pyrimidines 24. In acid 24 is produced, whereas under alkaline conditions 23 is the major product (60CB1106 62LA104). 

The reaction of 3-amino-2-pyrazolin-5-one with diketene afforded 2-hy-droxy-7-methyl-1,2-dihydropyrazolo[ 1,5-a]pyrimidine-5-one (49US2481466) (Scheme 1). 

The electrochemical oxidation of 4-dimethylaminoantipyrine (4-dimethyl-amino-2,3-dimethyl-l-phenyl-A3-pyrazolin-5-one) has been investigated in CH3CN-NaC104 at a glassy carbon electrode.421 The first step is a quasi-reversible electron transfer from the lone-pair electrons on the 4-dimethyl-amino nitrogen to form the radical-cation. The second-order disappearance of the radical-cation is presumably due to a disproportionation reaction. The oxidation at the potential of the plateau of the first wave gave the protonated 4-dimethylaminoantipyrine in 60% yield, but other products were not identified. 

Substituted pyrazolin-5-one heterocycles (187) have been coupled (Scheme 90) with a diazotized styrene-divinylbenzene copolymer (188) for purposes of forming a metal com-plexing resin (73MI11104). Resin (189) exhibited varying degrees of complexing ability with Cu +, Ni, Co, Mg2+ and Zn2+ ions. Selectivity was controlled primarily by the size of the R and R substituents. When R = Me and R = Pr1, for example, the resin exhibited a predominant selectivity for Cu2+ ion. 

A variety of heterocyclic systems have been used for forming merocyanines. The more usual nitrogen-containing heterocycles involved include benzimidazole, quinoline, ben-zothiazole, benzoselenazole, thiazole, thiazoline and indolenine. Among the more useful carbonyl-containing heterocycles are derivatives of 2-pyrazolin-5-one, 2-thiobarbituric acid, rhodanine and hydantoin. 

Several other classes of heterocyclic compound have been identified as alternatives to 2-pyrazolin-5-ones. Both the pyrazolo[2,3-a]benzimidazole (53) (59GEP1070030) and the pyrazolo[3,2-c]-s-triazoles (54 A, B = alkyl, aryl) (77JCS(P1)2047) give magenta dyes with low blue absorption. 

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